The Role of Plasmon Initiated Electron Transfer in Enhanced Raman Spectroscopy

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With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Zachary Schultz and his group at Ohio State University are investigating new ways to detect and quantify trace proteins and other biomolecules using lasers. The ability to detect specific biomolecules in real-world samples is important for identifying pathogens, tracking environmental pollutants, and monitoring disease. Specialized techniques called surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) use nanoparticles to increase the strength of the signals observed in some laser-based measurements. Currently, there are only a limited number of molecules that are readily detected using these techniques under ambient conditions and in complex systems. In order to address this limitation, the research team led by Dr. Schultz is working to better understand the mechanism that is responsible for the increased signals when proteins are in contact with nanoparticles by using a laser to illuminate individual proteins or protein fragments through a microscope. The goal of the research is to enable more sensitive measurements that will make it possible to detect and identify a much wider range of biomolecules. The project also addresses the need for a technically skilled and scientifically informed workforce by incorporating aspects of the research project into educational materials for the approximately 8,000 students who take general chemistry courses each year at Ohio State University. The project also provides valuable research experience for undergraduate and graduate students, and supports the Schultz laboratory’s collaboration with students and faculty in Chile, broadening student perspectives on the international nature and impact of science. The research team led by Dr. Zachary Schultz is testing their hypothesis that stable radicals formed from interactions with excited plasmon resonances on nanoparticles can transiently and selectively increase the Raman cross-sections of biomolecules in SERS and TERS measurements. The team’s experimental measurements suggest that such interactions occur, and even alter the observed SERS spectra of the amino acid tryptophan and some tryptophan-containing proteins. Imaging the SERS emission from a sample and applying super-resolution algorithms should allow the researchers to locate and identify individual molecules that are in contact with a nanoparticle. These measurements are expected to simultaneously resolve the SERS spectrum of the individual molecule, even in complex samples. The information the team obtains from these sophisticated measurements should enable them to identify proteins and other biomolecules that exhibit increased sensitivity, and also enable them to better understand what makes such enhancements possible. Based on the improved understanding of the mechanism for SERS and TERS enhancements, the outcomes of this research can help guide the development of new and improved chemical sensors that are important for a very wide range of applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.